The present invention relates to a valve timing control apparatus for an internal combustion engine, which variably controls opening and closing timings of an intake valve and/or an exhaust valve of the engine, for instance, by using a hysteresis brake.
Japanese Patent Application First Publication No. 2004-156508 discloses a valve timing control apparatus for an internal combustion engine including a timing sprocket to which a rotational force is input from an engine crankshaft, a camshaft supported so as to be rotatable with respect to the timing sprocket within a predetermined angular range, a sleeve connected to the camshaft, and a rotational phase adjusting mechanism for adjusting a relative rotational phase between the timing sprocket and the camshaft which is disposed between the timing sprocket and the sleeve.
The rotational phase control mechanism includes a radial guide window formed in the timing sprocket, a spiral guide (a spiral groove) formed in a disk plate, a link member having one end portion rotatably disposed on the sleeve and the other end portion radially moveably disposed in the radial guide, an engagement portion disposed on the other end portion of the link member and engaged at a distal end thereof with the spiral guide, and a hysteresis brake that applies a braking force to the disk plate depending on the engine operating condition.
An electromagnetic braking force is applied to the disk plate through a hysteresis material by energizing an electromagnetic coil of the hysteresis brake. Owing to the electromagnetic braking force, the engagement portion is radially moved along the radial guide window and slided along the spiral guide to thereby cause relative rotation of the timing sprocket and the sleeve (the camshaft) within a predetermined range of angle and variably control opening and closing timings of the intake valve in accordance with the engine operating condition.